Then there are prospects who seem to have “future star” tattooed on their foreheads. Like Poe and Blackmon.

That high-risk, high-reward potential is why we love the draft. Who knows what players like Poe and Blackmon are going to be as pros? Nobody. If a team’s instincts are right, Poe will be the N.F.L.’s next great pass rushing nose guard and Blackmon will be the next Larry Fitzgerald. If they get it wrong, they are Dewayne Robertson and Michael Crabtree.

But when was the last time you heard that debate about a linebacker or a running back? Not since LaVar Arrington (bust) and Adrian Peterson (most definitely not) has the issue been raised. And this year is no different.

Luke Kuechly, the linebacker/tackling machine from Boston College, and Trent Richardson, the tackle-breaking running back from Alabama, are two players most pundits are labeling “can’t miss.” Is it because of their combination of size and speed? Or because they performed well at the combine? Their intangibles?

No.

It is because both are very good at playing positions that are increasingly devalued in today’s N.F.L. Unless you are a quarterback, a guy who can stop the quarterback (defensive end) or a guy who protects the quarterback (left tackle), then really you are there for decoration. That can make things tricky for teams looking for the next pass-rushing nose guard or All-Pro receiver. So if you are the Bills sitting at No. 10 and both Poe and Kuechly are still available, do you gamble on a boom-or-bust prospect or make a safer pick? The answer is, you roll the dice and take Poe.

That is because players like Kuechly and Richardson are going to make their living playing on first and maybe second down. Neither is likely to play much on third down, which is when many games are won and lost. Players like Poe and Blackmon will. Kuechly and Richardson are elite athletes who will play roughly 20 to 25 snaps a game, but being viewed as safe means that even if they are starters, they are going to spend plenty of time on the sideline.

When the spread offense began to dominate college football about a decade ago, it was intended to get big, 260-pound linebackers away from the line of scrimmage, so a team could run the ball up the middle for four yards. But as the spread offense started to evolve, it was no longer focused on merely fooling defenses, but on exploiting them.

Photo

Teams are likely to take a chance on Oklahoma State receiver Justin Blackmon, right, who could become a game-changer, or not.Credit
Paul Connors/Associated Press

Defenses had to adjust, and those 260-pound run-stoppers were suddenly asked to learn how to line up with their hand on the ground and rush the quarterback, and linebackers became 225-pound hybrids who could run with wide receivers, blitz when asked and make the occasional tackle on a running play.

When Florida State’s linebackers started weighing 220 pounds, it was inevitable that the N.F.L. would soon follow the trend. Jordan Senn, who started seven games for the Carolina Panthers last season and is all of 5 feet 11 inches and 220 pounds, is just one example. There are more players like him than there are like Levon Kirkland, the nearly 300-pound behemoth who played linebacker for the Pittsburgh Steelers in the 1990s.

To be fair, Kuechly is a great prospect. But even at his peak, is he going to be seen as a game-changer? Probably not. That is because linebackers in today’s N.F.L. are really tweeners. They are in between the important players. This excludes hybrids like the Steelers’ James Harrison, who are linebackers in name only, but really smaller versions of pass-rushers like Julius Peppers. Today’s game is about specialists. And unless a traditional linebacker is blitzing or covering Rob Gronkowski (which most of them are unable to do), they are not doing anything all that special.

So once Kuechly gets to the N.F.L., no matter how good he is, offensive coordinators will not lose sleep worrying about him. But that’s O.K. They don’t lose sleep over Ray Lewis or Brian Urlacher either, because with certain formations, they can get Urlacher replaced by a defensive back. At no point can they do that with a quick pass-rushing defensive end like Justin Tuck.

Last season there were only 15 teams with 1,000-yard rushers. Eight of those teams had a back who barely surpassed the mark, which means they all had a back who averaged at least 62.5 yards a game. That is a stark contrast from even five years ago, when 23 teams had backs who ran for more than 1,000 yards.

It has reached a point where most teams don’t even have a fullback; what used to be a change-of-pace back is now a full-time back. That is because today’s N.F.L. means changing the pace on every down.

So if you’re pining for the days of Roger Craig slamming into Mike Singletary after 3 hard-earned yards, go play Tecmo Bowl. Today’s version of Craig is streaking down the sideline as a wide receiver, and Singletary has been replaced by a kid who ran the 4x400 relay in high school.

Either way, sometime this fall, Kuechly and Richardson are going to stare at each other from across the line of scrimmage on first down. If they collide, it will demonstrate the principles on which the N.F.L. was built.

Then it will be second-and-7, and both Kuechly and Richardson will trot to the sidelines, replaced by the smaller, more versatile players around whom the game is now built.

Welcome to the N.F.L., rookie.

Trevor Pryce, a former N. F. L. player, is a producer and the author of “An Army of Frogs: A Kulipari Novel,” to be published next spring.

A version of this article appears in print on April 27, 2012, on page B11 of the New York edition with the headline: For N.F.L. Seeking Specialists, an Army of Extras. Order Reprints|Today's Paper|Subscribe